1. Field of the Invention
The present invention generally relates to a brushless motor suitable for use in a video apparatus, an audio apparatus, or the like, and more particularly to a wiring structure of drive coils mounted on a stator yoke at a stator portion in such a brushless motor.
2. Description of the Prior Art
Conventionally, such a brushless motor as shown in FIG. 5 has been widely used for driving a head cylinder of a VTR, or the like.
In FIG. 5, a brushless motor is provided with a rotor portion 1 and a stator portion 2.
The rotor portion 1 is constituted mainly by a cup-like rotor yoke 3, a ring-like rotor magnet 4 fixedly bonded to the inner bottom portion of the rotor yoke 3, a ring-like frequency generator magnet 5 (hereinafter, referred to as FG magnet) disposed inside the rotor magnet 4 and fixedly bonded to the inner bottom portion of the rotor yoke 3, and a rotary shaft 7 passed through the rotor yoke 3 as well as a connector member 6 at the center axis portion and secured thereto. The rotor magnet 4 and the FG magnet are divided into pieces which are circumferentially successively magnetized to be N-pole, S-pole, N-pole... S-pole and arranged to be exposed from above as shown in the drawing.
The stator portion 2 is constituted mainly by a disk-like stator yoke 8, a plurality of drive coils 9 mounted on the stator yoke 8, a disk-like FG basic plate 10 fixedly bonded to the drive coils 9, and a wired substrate 11 mounting drive circuit parts (not shown) and fixed to the stator yoke 8 above the stator yoke 8 by means of screws. An FG coil (not shown) constituted by digital conductive patterns circumferentially continuously connected is formed on the FG basic plate 10 and the FG coil is provided in the magnetic field between the FG magnet 5 and the stator yoke 8.
Two pulse generator magnets 12 and 13 (referred to as PG magnets) are fixedly bonded to the outer periphery of the rotor yoke 3 at opposite positions opposed to each other, that is angularly separated by 180 degrees from each other. The PG magnets 12 and 13 have outwardly exposed faces of magnetic poles different from each other. A PG head 14 for detecting magnetic flux from the PG magnets 12 and 13 is mounted on the stator yoke 8.
Fig.6 is a segmentary enlarged plan view showing the state in which the drive coils 9 have been mounted on the stator yoke 8. As shown in the drawing, a plurality of coil holders 15 each formed in a substantially trapezoidal shape in plan are projectingly provided through outsert molding on the stator yoke 8 at predetermined positions. Each of the drive coils 9 having a number of turns is positioned by a corresponding one of the coil holders 15 and fixedly bonded to the stator yoke 8. An inside wire terminal of each drive coils 9 is passed through a through hole 15a of the associated coil holder 15 and fixedly soldered to the wired substrate 11 and an outside wire terminal of the drive coil 9 is passed through the stator yoke 8 and fixedly soldered to the wired substrate 11.
In FIG. 5, illustrated are a lower cylinder 16 which constitutes a fixed side of a head cylinder of a VTR and a bearing 17 provided on the lower cylinder 16. The stator yoke 8 of the stator portion 2 is fixed on the lower surface of the lower cylinder 16 by screws and the rotary shaft 7 of the rotor portion 1 if fixedly attached to an upper cylinder (not shown) which is a rotary side of the head cylinder.
In the thus arranged conventional brushless motor, when the drive coils 9 are supplied with a drive current from a drive circuit provided on the wired substrate 11, electromagnetic force is generated by interaction between the drive current and magnetic flux from the magnetic pole faces of the rotor magnet 4, so that rotary force is generated in the rotor to thereby rotate the rotor portion 1. Consequently, counter electromotive force is generated in the FG base plate 10 due to changes in magnetic field because of rotation of the FG magnet 5 and taken out as a frequency signal, whereby the rotary speed of the rotor portion 1 is controlled to rotate at a fixed speed in response to the frequency signal. Upon rotation of the rotor portion, the PG head 14 successively receives magnetic flux from the PG magnets 12 and 13 which rotate together with the rotor yoke 3 and produces a PG pulse every 180 degrees in one revolution of the rotor portion 1, whereby the phase of the rotor portion 1 is detected on the basis of the PG pulse.
In the conventional brushless motor, however, there are disadvantages that the inside wire end of each drive coil 9 positioned by the coil holder is apt to come loose if tensile force acts thereon because there is no measure to prevent such tensile force, and therefore each drive coil 9 comes loose at the soldering of the wire terminals of the drive coil 9 to the wired substrate 11, or in the mounting of the stator portion 2 onto the lower cylinder 16.